In persons with cystic fibrosis (CF), thick, purulent secretions contribute to airway obstruction and bacterial infection. One of the mainstays of CF therapy is to clear the airways of these secretions. Recent studies have found that aerosolized hypertonic saline (HS) has enhanced mucociliary clearance and improved lung function in CF patients treated over two weeks. However, the effects of HS on sputum microbial flora and airway inflammatory mediators have not been examined. Since respiratory infection in CF is thought to be related to increased airway salt concentration, HS has the potential to cause increased infection. We propose a placebo-controlled trial of aerosolized HS in CF over two weeks to confirm its efficacy, and examine its impact on respiratory infection and airway inflammation. We hypothesize that HS will improve pulmonary function without causing an increase in bacterial density, elastase activity, or interleukin-8 levels.